I used a regular no frills brand of sf cherry lime drink powders. I bought mine at walmart.
The first few days didn't feel challenging. I began my fast on the weekend so I could sleep through the first two days. From then it didn't feel like I was 'fasting'. I didn't have a sudden urge to break fast. The flavoring seem to just make me forget that I was fasting. It felt like any other day except for the occasional headache.